Bubble construction for expansion chucks



y 27, 1954 G. HOHWART ETAL 2,684,854

BUBBLE CONSTRUCTION FOR EXPANSION CHUCKS Filed Feb. 23, 1952 INVENTORS.8 fizzy/4,2 1/ 5 M5? WW4? Patented July 27, 1954 BUBBLE CON STRUCTIONFOR EXPANSION CHU George Hohwart, Farmi County, and Ernest F Mich.,assignors to N. Ferndale, Mich., a co 4 Claims.

This invention relates broadly to new and useful improvements inchucking devices.

An important object of the present invention is to provide an improvedmanufacture for chucks of the type disclosed in our copendingapplication Serial No. 119,192, filed October 1, 1949, now Patent No.2,626,811.

Other objects and advantages of the invention will be apparent duringthe course of the following description.

In the drawing forming a part of this specification and wherein likenumerals are employed to designate like parts throughout the same,

Fig. 1 is a longitudinal sectional view showing a chuck embodying theinstant invention mounted on an operating cylinder and operativelyassociated with a workpiece,

Fig. 2 is a view similar to Fig. l but showing the chuck separate fromthe operating cylinder and the workpiece and illustrating anintermediate step in the manufacture of the chuck,

Fig. 3 is a fragmentary transverse sectional view taken on the line 3-3of Fig. 1, and

Fig. 4 is a fragmentary, longitudinal sectional view illustrating acritical defect in the prior construction that has been corrected by theinstant invention.

As suggested, the invention is concerned primarily with a chuck or arborof the type disclosed in the copending application referred to above.This chuck is generally tubular in form and has one or morelongitudinally arched clamping sections or bubbles which expand orcontract to clamp a workpiece when the chuck is stressed axially. If thework is to be clamped on the outside of the chuck the clamping sectionsare arched outwardly; but on the other hand, if the work is to beinserted into the chuck the clamping sections are arched inwardly.Preferably, the clamping bubble or bubbles engage the work when thechuck is relaxed or unstressed. Thus, in use, the chuck is placed undertension to contract the bubbles suificiently so that the work can bemoved either over or through the bubbles as the case may be. Then whenthe chuck is released, the bubbles expand into clamping engagement withthe work.

It is believed that the above construction can best be illustrated byreferring to Fig. 1 of the drawing which shows a tubular chuck Iembodying the invention attached to the forward end of a cylinder I2 inwhich a piston i4 is reciprocally mounted. The piston I4 ispoweractuated forwardly in the cylinder I2 in any suitable manner, andas it advances it pushes against a pin it between the piston and thedistal end of the chuck I0. Thus, the piston pushes against the pin Itto stretch the chuck I 0, and as the chuck stretches it reduces thediameter of the bubble section I8 sufliciently so CKS ngton Township,Oakland ederick Hohwart, Detroit,

A. Woodworth Company, rporation of Michigan Application February 23,1952, Serial No. 273,107

2 that a workpiece can be slipped onto the chuck as shown in thedrawing. When power against the piston I4 is released, the inherentresiliency of the chuck I0 causes it to assume its former position andthe bubble section I8 to expand against and tightly clamp the workpiece20.

With the above general introduction, it will be observed that theparticular chuck I!) here shown has a relatively heavy base portion 22at one end thereof which is adapted for attachment to the cylinder I2.The chuck II] is properly centered with respect to the cylinder by theinner terminal 24 of the base portion 22, which terminal extends intoand snugly fits a central opening 2% in the cylinder I2. A radial flange28 on the base portion 22 overlies the cylinder I2 around the opening 26and is securely but detachably fastened to the cylinder by screws St).

The cylinder I2 here shown comprises a generally cup-shaped member 32which is piloted in an annular groove 34 provided in a base plate 36.Screws t8 detachably fasten the cup-shaped member 32 to the base plate36. Screws in turn fasten the base plate 36 to a spindle 42 or the like.

The piston I4 is free-floating in the chamber 44 of the cylinder I2, andthe space between the periphery of the piston and the inner annular wallof the cylinder is sealed by an O ring 48. Any suitable means may beused for driving the piston I4 forwardly in the cylinder I2, and by wayof illustration, apparatus which is pneumatically operated ishere'shown. To this end we have shown an air pipe 48 extending through alongitudinal passage 50 in the spindle 42 and threaded into an opening52 in the backing plate 36. The pipe 48 extends from any suitable sourceof air under pressure and delivers the air into the cylinder chamber 44behind piston I4. Air pressure in the chamber 44 acting against thepiston I4 drives the latter forwardly against the pin IE to operate thechuck In in the manner hereinabove described.

Heretofore the bubble section I8 of the chuck It has been formed in twoparts 54 and 55 as shown in Fig. 4, and the two parts have been joinedby an inner, relatively thick ring 58. The usual practice has been toform the ring 58 with a centrally disposed outwardly extending rib whichextends between the two sections 54 and 56 and terminates flush with theouter surfaces thereof. When the chuck is made, the ring 58 fits snuglywithin the two bubble sections 54 and 56, and after the parts areassembled as shown in Fig. 4, the inner ring 58 is copperwelded to thesections 54 and 56 to form an integral one-piece construction.

The above construction has been generally satisfactory but is relativelyshort-lived. More particularly, it is subject to the disadvantage thatwhen the chuck is stressed longitudinally to reduce the diameter of thebubble section It sufficiently to receive the work 20, the two parts 54and 56 of the bubble tend to assume the positions shown in Fig. 4. Thiscreates excessive stresses in the copper-weld joint between the parts 5dand 56 and the ring 58 so that repeated fiexure of the chuck l rupturesthe copper-weld material. When this occurs, the parts come apart or,alternatively, the copper-weld joint merely fractures sufficiently sothat the chuck becomes faulty in operation.

We have now discovered that if the bubble section IQ of the chuck if! ismade as shown in Fig. 2 the above difficulties are obviated.Specifically, the bubble part 56 is made with a frusto-conical outersurface '62, which surface tapers toward the end of the part, and thepart 5-5 is made with a similar frusto-conical inner surface 6% whichtapers away from the end of the part. The tapered terminal portion ofthe part 56 fits snugly in the correspondingly inwardly tapered terminalportion of the part 5 3, and the two surfaces 82 and 54 exactly coincideas shown in the drawing.

It will be observed that this construction provides a tapered interfacebetween the parts 54 and 56 and that this interface extends obliquely ina straight line from substantially the outer surface to substantiallythe inner surface of the bubble it. The parts preferably arecopperwelded together in order to units the two sections 54 and 55 andin order to provide for the necessary unitary construction.

The outer section 54 is constructed initially to extend beyond theengaged surface of the inner section 56 as perhaps best shown in Fig. 2.The extending portion 56 provides a trough 68 which receives a copperweld wire H3. The chuck it is then placed on the end 72 thereof in asuitable furnace and heated to a temperature which causes the copperweld wire Hi to melt and flow downwardly along the interface 62-6d. Thecopper-weld thus formed effectively unites the two parts 54 and 56 toform an integral onepiece construction. After the copper weldingoperation, the projecting portion 56 is cut off and the bubble isreduced to the desired final size and form to provide a finishedconstruction, as shown in Fig. 1.

When the parts 54 and 56 are constructed and joined together in themanner thus described, the life of the chuck is greatly increased. Wehave found that a chuck constructed inthis man-- ner can be flexed many,many times without danger of a ruptured or fractured joint between theparts of the bubble. It will be observed that the relatively thinfeather edge of each part 54 and 58 is disposed adjacent to a relativelyheavy or thick portion of the adjacent part. Apparently when the chuckis flexed in use the relatively thin feather edge of each sectionfollows easily and conforms readily to the stressed shape of the chuckand any tendency for the individual sections to resist fiexure andfracture the copperweld joint which unites them is substantiallyeliminated. In any event, actual tests have shown that the instantconstruction extends the life of the chuck many fold.

In this connection it will be readily appreciated that the expressionfeather edge does not mean that the taper ends of the parts 54 and 56must come to a thin knife edge. This expression is intended to includethin taper ends of the type shown in the drawing but notnecessarilysharp taper ends. The important thing in so far as theinstant invention is concerned is that the taper construction reduce theresistance offered by the taper ends of the parts 54 and 5B suflicientlyso that they flex readily with the arbor section of the chuck. When thisresult is accomplished, the taper ends of the parts offer no appreciableor significant resistance to flexure of the chuck and minimizepossibility of rupturing the diagonal joint defined by surfaces 62 and64.

Having thus described the invention, we clai 1:

l. A chuck arbor comprising a tubular secti having a longitudinallyarched, radially expai sible portion having a plurality of longitudinalthrough slots spaced circumferentially therearound, the latter beingformed from two interfitting parts and said parts being separated by afrusto-conical interface which extends obliquely from the outsidesurfaces to the inside surfaces of said parts and defines a relativelythin feather edge on each of said parts, and means integrally unitingthe parts at said interface.

2. A chuck arbor comprising a tubular section having a longitudinallyarched radially expansible portion having a plurality of longitudinalthrough slots spaced circumferentially therearound, the latter beingformed from two interfitting parts and said parts being separated by afrusto-conical interface extending obliquely from the outside surfacesto the inside surfaces of said parts and defining a relatively thinfeather edge on each of said parts, and copperweld material along theinter-face between said parts bonded to and integrally uniting saidparts.

3. A chuck arbor comprising a tubular section having a longitudinallyarched radially expansible portion having a plurality of longitudinalthrough slots spaced circumferentially therearound, the latter beingformed in two parts,

. one part having an external conical surface extending from one endthereof and the other part having an internal conical surface extendingfrom one end thereof, the conical surfaces of said parts defining anessentially thin feather edge on each of said parts and the conicalsurfaces of each part flatly engaging the conical surface on the otherof said parts, and means integrally uniting the mentioned conicalsurfaces of said parts.

4. A chuck arbor comprising a tubular section having a longitudinallyarched, radially flexible portion having a plurality of longitudinalthrough slots spaced circumferentially therearound, said flexibleportion being formed of two parts having relatively long overlappingtapered portions defining a diagonal interface extending between theinner and outer surfaces of said section, and metal in the joint betweensaid tapered portions integrally uniting said parts, the taper end ofeach of said tapered portions engaging and being relatively thin withrespect to the adjacent part of the other of said portions and. flexingreadily therewith in use so as to minimize resistance of said taper endsto flexure of said chuck and consequently to rupture of the brazed jointbetween said parts.

Number Name Date Davis Oct. 31, 1939

